What Is a C-Reactive Protein Test?

Medically Reviewed by Jabeen Begum, MD on November 29, 2021
3 min read

If you have high cholesterol, you've probably been told to lower the LDL number from your blood test. LDL is the "bad cholesterol," the type that contributes to plaque that can clog your arteries. This can lead to a heart attack or stroke.

But that's only part of the story. Research shows that only 50% of people who suffered heart attacks had high LDL levels. So, many doctors use another test called the C-reactive protein test to help figure out who’s at risk.

C-reactive protein (CRP) is produced by the liver. Its level rises when there is inflammation in your body. LDL cholesterol not only coats the walls of your arteries, but it also damages them. This damage causes inflammation that the body tries to heal by sending a "response team" of proteins called "acute phase reactants." CRP is one of these proteins.

One study found that testing for CRP levels is a better indicator of cardiovascular disease (CVD) than the LDL test. But, it's important to know that a CRP test is not a test for heart disease. It's a test for inflammation in the body.

The test is also used for people suffering from autoimmune diseases like lupus and rheumatoid arthritis. They also cause inflammation. A doctor might test someone with either condition to see if anti-inflammatory medication is working, though the CRP test cannot determine where the inflammation is taking place.

A variation of the CRP test, the high-sensitivity CRP (hs-CRP), is used to check for cardiovascular disease.

It’s a simple blood test. A sample is drawn from a vein, most likely in your arm. No special preparation is needed (like fasting) and the test is not painful beyond a sting on the arm from where needle is inserted. The test may be affected by medications you take, so ask your doctor if you need to cut back beforehand. The blood sample is tested at a lab.

Here are what the results mean:

  • hs-CRP level of lower than 1.0 mg/L -- low risk of CVD (heart disease)
  • hs-CRP level of 1.0 mg/L and 3.0 mg/L -- moderate risk of CVD
  • hs-CRP level of more than 3.0 mg/L -- high risk of CVD

A high level could also be a sign of cancer, infection, inflammatory bowel disease, lupus, rheumatoid arthritis, tuberculosis, or another disease. It could also be high because you're in the second half of your pregnancy or you are using birth control pills.

The hs-CRP test is most useful for people who have a 10%-20% chance of having a heart attack within the next 10 years. The test is not helpful for people with a higher or lower risk.

Because your CRP level can vary, the test should be done two times (2 weeks apart) to determine your risk of heart disease. It’s also important to remember that you could have a high reading without necessarily having heart disease. So, it's important to check your LDL levels as well to get a full picture of your CVD risk.

Fortunately, the same statin medications that lower LDL have also been shown to lower CRP levels. In addition to any medicine, you should make some lifestyle changes (cut down on fatty foods, stop smoking, and start exercising) at the same time.